Guestblogging and other ways to create content

Because the most tips I read so far are on blogtechniques and earning money, here another topic: how to get your blog juicy by creating blog journeys!

Last weekend I came accross the Carnival of the Capitalist (see Blog trektocht). Here I first encountered a way to get themes from seperate bloggers and spirits together. The ‘normal’ way I thought about is was to invite guestbloggers. There also is a Carnival of the Vanities on politics , culture etc. (Here you’ll find issue 152)
A friend from the medical department pointed me to the latest issue of Grand Rounds. This is common medical practice, put in a weblog-format. (An archive can be found here) Every week another medical site is host. GREAT.
This seems to be a perfect way to get fresh thought for your own theme!

So some questions to get a discussion going:
do you know other examples?
do you have experience in participating in such a blogjourney?
Are you willing to participate? (and if no why)